Xerographic type copiers using reciprocally movable carriages to provide scanning of a document or thing to be copied have been known for many years. Typically, these carriages have either held the optics such as lenses and mirrors which are moved so as to scan a fixed document, or have retained the document itself so as to move it past a fixed scan window and optic coupler. U.S. Pat. No. 2,959,095 is an example of the latter type of scanning system.
It is generally preferred, especially for low cost copiers, that the drive motor concurrently operates as many of the machine elements as possible. Frequently such systems employ mechanical and/or electromechanical switching elements that rapidly reverse the direction of traverse of the carriage. For low speed or table-top copiers, simple switching devices are preferred for this function because they minimize both cost and carriage reversal time. Unfortunately, such devices also cause brief deviations of power application to the other copier components because of the carriage inertia. This is not overly detrimental for systems wherein the image is directly transferred from the original document onto a photosensitive copy sheet, since image transfer is complete before carriage reversal occurs.
However, the result is different for systems using photoconductive belts or drums to receive the image which is carried for some distance from the imaging station (usually including some intermediary operation such as development) to the point of transfer to a copy sheet. Such systems frequently produce a short band of blurred copy on the copy sheet because the transfer function is still in progress at the time of carriage motion reversal unless the carriage scan motion is carried out excessively or the distance from image to transfer stations is made long enough so that transfer has not started at the time of carriage reversal. The two latter-mentioned options are unacceptable, particularly for compact, low cost copiers.
The only arrangement known in the prior art for decoupling the adverse effects of the reciprocating carriage motion reversal from the remainder of the machine operation is shown in U.S. Pat. No. 3,697,165 by Morriston et al. where the carriage is driven by a slotted link and link pin connected to follow motion of a closed loop chain. Separate switches at the 90.degree. turns on each end of the chain reverse the drive motor coupling to the chain. This configuration is intended to cause direction reversal of the carriage at approximately the zero horizontal motion point of the yoke and link pin. Such a system requires acceptance of a substantial cost penalty for the additional parts, switches and circuitry.
Various shock absorbing mechanical couplers have also been known in the past, Lewis et al. U.S. Pat. No. 2,071,885 being one example. Lewis et al. shows retained springs to provide mechanical coupling between radial ears of driving and driven hubs. Despite the presence of such couplers in the prior art and the continued presence of the copier quality degradation problem stemming from carriage motion reversal, the prior art is devoid of any suggestion that the problem is resolvable through a combination in accordance with the present invention as described below.